Wireless communication systems have become pervasive and ubiquitous to the point where data rate and quality of service requirements have become comparable to those of wired communication systems. Next generation wireless systems incorporate multiple-input multiple-output (MIMO) techniques to achieve their performance goals. MIMO systems promise higher channel capacities compared to single antenna systems by exploiting the spatial characteristics of the multipath wireless propagation channel. The theoretical performance gain achievable by MIMO systems is limited due to a number of practical design factors, including the design of the antenna array and the amount of inter-array element mutual coupling. While mutual coupling can be alleviated by increasing the spacing between array elements, accommodating multiple antennas with large spacing in modern consumer devices may be impossible due to stringent space constraints. In order to meet such demanding, and often contradictory, design criteria, antenna designers have been constantly driven to seek better materials on which to build antenna systems.
As disclosed in U.S. Pat. No. 6,933,812, metamaterials are a broad class of synthetic materials that could be engineered to wield permittivity and permeability characteristics to system requirements. It has been theorized that by embedding specific structures (usually periodic structures) in some host media (usually a dielectric substrate), the resulting material can be tailored to exhibit desirable characteristics. These materials have drawn a lot of interest recently due to their promise to miniaturize antennas by a significant factor while operating at acceptable efficiencies.